Optical molecular imaging of breast cancer using targeted fluorescent contrast agents has been demonstrated by several research groups; however, these applications generally involve imaging of single contrast agents. The objective of the proposed research is to enable non-invasive multi-label optical molecular imaging of multiple exogenous cancer markers, using fluorescence lifetime imaging (FLIM) to discriminate multiple contrast agents with overlapping emission spectra. The use of multi-label FLIM in molecular imaging has the potential to enable simultaneous imaging of many more contrast agents in vivo, which has important implications in the study, diagnosis, and prognosis of human breast cancer. Specific Aim I. Construct a model molecular system for multi-label FLIM and demonstrate feasibility of the approach in solution. Specific Aim II. Demonstrate selective targeting of contrast agents to multiple molecular breast cancer markers in cell culture, and demonstrate multi-label FLIM of the agents after binding with molecular targets. Specific Aim III. Perform the goals of Aim II in vivo in murine and human mammary tumors in the mouse. [unreadable] [unreadable] [unreadable]